Means for electric-energy translation



Jan- M, i930 J. L. FEARING MEANS FOR ELECTRIC ENERGY TRANSLATION www@ 5am M, i930. J. 1 HEARING f743443 MEANS v FOR ELECTR I C ENERGY TRNSLAT ON Fi led OG t l l 1923 2 She e QS-She@ t 2 HVIVU AVAVAVAV 'A'AYAVM lllllllll SOURCE VVVVVVVVV Jus'riri i3. irnnnrne, on sovra WEYi/ionrii p ,irnssaonnsn'r'rs -assieivon fre nnncrnic sonreir?, moon-rouwen, or new venir, ri. ir., ,a connor.; lori ce 'lunaire non unserern-minnen realiseer-rioni application led October li, 392%. Serial No. @GW/Se.

This invention relates to means for electric energy translation. Y

An object' of-this invention is to control a source of supply of electric energy in accordance with electric currents or electrometive forces of critical value. f I

Another objectof the invention is to produce motion of an indicator corresponding to the va liations oan impressedrvave,

An additional object is to render. possible ana-lysis of an electric Wave bycompari-ng its instantaneous values with a standard source oi electric energy.

.il further object is to protect electrical circuits and associated apparatus against electroniotive forces or currents o'l predetermined value. y

-l feature of this invention relates to automatic circuit control characterized by lack of inertie and-by substantially instantaneous response.

An additional eatureconcerris a. circuit protective device having no moving contacts in the circuit to be protected. f

A further feature of the invention relates to' an amplifier of electric energy which is responsive to control currents or electromotive forces of small or large amplitude over a Wide range of frequencies.

A still further Jfeature relates to an energy control circuit iitilizingvacuum tubes, which control circuit Yis responsive to sharp impulses. l

Another feature of this invention is an ampliiier capable of beingtriggered by im-v amplifier. These mechanical devices may, 55 in certain instances, consist of means tor in dicating the forni of the impressed elecitromotive :torce or current. ln other instances they may consist oit electriccircuit control* 4'lei-s, as for example protective devices such @e that when the input voltage orcurrent exceeds a'given value7 the source ci energy may be disconnected. f f l This invention may be applied in another manner for the purpose of analyzing an inapressed Wave by controlling from the ampliier output circuit7 an indicator mechanism which may ,be made responsive vte instann taneous peaks in the Wave te be analyzed.

rlliis lmay be done by impressing the Wave 7e under analysis upon the amplii'ier and simul taneously upon an auxiliary circuit, in which auxiliary circuit the phase oi the impressed Waves is shifted., whereby the indicator is caused to besensitive and to give an indica- 75 tion of the peakA existing during a very short interval o time. l l

The drawings Which are referred to in the detailed description which follows are illustrative of certain embodiments and certain eo siniilarto that of Fig. 'i in which the ampliy Se er is conductively independent oi the circuit to be protected; Fig, 3, an application of this invention to a signaling system.

Fig. 1l, an embodiment similar to Fig. 3 e@- applied as a means of remote control.

Fig. 5, a circuit in which t ie invention is applied as means for producing a graph ci the torni or an impressed Wave.

Fig. 6, an adaptation ci the invention as a o5 wave analyzer. l

Fig. i', a curve illustrating the adjustment of the grid potentials on the various tubes of the amplier oil. this invention.

Lilie reference characters have been used 10o 17, which ispconnected between its grid and cathode and which comprises grid polarizing battery. 20 and series resistance 21, maybe con- 'nected by means of switch 22 acnossthe res-istance 24 in series'with the transmission'line 1101' across the resistance 25 shunted'across the transmission line l1. The input circuit of'tube 17 is shown connected to resistance tubev17.

wherebyany variationin the potential of thesource 14 supplying energy to the transmission lineisimpressed upon t'hgrid of The output circuit of tube 17 comprises battery 26 in series'with a coupling resistancie feo 27. The input circuit of tube 18: cho nnc gs` across the resistance 27 and .includes at- Y tery 29 for producing a normal polarization of its grid. vThe output circuit of tube 18 connected between its plate and filament may ,be traced as follows: plate of tube 18, battery 53, closed contacts of switch key 30, re-

"sistance 31, positive side of transmission i line 11, resistance 21, to the filament of tube 18.

The input circuit of tube 19 connects across the coupling resistance 31 in the output circuit of tube 18 and is also provided with a grid polarizing battery 32. i The -output circuitv I of tube 19 which includes its plate and filamentv is connected in series with the positive side of the transmission line 11.

A fourth three-electrode tube 34'hasits in'- pu-t circuit including its filament and grid connected also across resistance 31 and is also provided with a grid polarizing -battery 35, The output circuit of this tube containsa battery 36 which supplies energy to an indicating device 38, which may be, for example, a galvanometer.

Afswitch- 39 has its terminals connected in shunt tothe output circuitvo-t-ulee V19 andthe platefllament path of this tube may be shortcircuited by a closure of the switch.

Energy source 14,-for example a battery, is connected to the transmission line 11 yby means of switch 40. Byopening this switch, battery 14 may be disconnected and by closing the corresponding switch 41 or 42, the

alternating current generator 13 or the direct current P l- Y When the input circuit of amplifier 10 is generator 12 may be connected in its connected by switch 22 across resistance 25 Vwshown, thefsysterngis-ajgranged to protect the transmission line l1 against excessive electrolnotive forces. -The polarizing loat-` tery-2O is adjusted to such value that the grid of tube 17 will be ma-intainedat a potential such that current Hows in. the output circuit of this tube (see 3 Fig. 7) unless a given electromotive force in the transmission line 1'1 1s exceeded. vWhen the .electromotlve force across reslstance 25 exceeds a predetermlned value, the ,potential of the grid ofl tube 17 will becomeless positive or more negative and will thuscause a reductonin the flow of current in the output circuitof the tube. -This circuit flows through resistance 27 and produces a decrease `in the potential drop thereacross. This .changeof potential is effective in the input circuit of tube 18 in decreasing the negative polarity or increasing the positive polarity of thegrid ofthis tube,.whereby a resultant increase in the current in the output circuit of tube 18v is produced. The resulting increase in potential across resistance 31 forming the coupling between` tubes 18 and 19 causes the grid of tube 19 to be negatively polarized. The impedance ofthe lament plate path of this tube is thus increased and the ,currerit'the'rein decrea sel.

For the purposes of this invention, it is proposed to adjust the variouselements of amplifierv 10 ,to such values that the potential impressed upon the grid of tube 19 when a predetermined voltage is exceeded in transmission line 11 will be sufficiently negative to completely block tube 19` (see 1 Fig. 7).

This blocking action will vtake place instantaneously because of the large negative potential built up on the grid of tube 19, by regenerative action. Regenerative action in the' ampliieris produced bythe coupling -resistance 21 in common to the output circuit of tube 18 and the input circuit of tube 17 whereby the chan e of current in the output circuit acts on tie input circuit to produce a still greater change. i

The effect of blocking tube 19 when switch 39 is open will be equivalent to openingthe circuit of the transmission line' 11. The power source 14 is thereby disconnected and the damage which might result from the excessive voltage is prevented.'

' The increase in current in resistance 31 and the resulting increase in potential across its terminals causes the grid of tube 34 to receive anincrease' of negative charge or a decrease of positive charge, whereby a change iny the current in its output circuit and consequently in the indicating device 38 is pro-A duced. Device 38, therefore, gives an indica-y tion'of the fact that the predetermined voltage has been exceeded'in the transmission line 11. r

The block 15 represents any energy consuming device which may be inductiveor noninductive' as, for example, an'electric lamp or vacuum tube filament circuit.

The amplier 10 may be arranged to protect the transmission line 11 from excessive the transmission line. lBy properadjustment of thewvalues ot the various elements.

of? the amplifier 10, it may be caused to re-Y spend to a critical value'ot current in resistance 2li such that when this current is reached or exceeded in the line 11, tube 19 Will block (see 1 vand will stop the oW of cur-A rent in the' lineas already described. The :tact that this current has been exceeded Will also be indicated by device 38 on account of change of current'which results in the output circuit ot tube in Fig. 2, the transmission lineill is sup' 11 by means ot variable transformer 51 and its output ,circuit inductively associated with line 11 by meansof transformer 52.

rlhe amplifier 50 comprises three-electrode vacuum tubes 17 and 18, resistance coupled in tandem in a manner similar to corresponding tubes of an'iplilier 10. The output circuit of tube 18 which is connected between its filament and plate electrodes includes a battery 53, switch lrey 30, resistance 31 and resistance 21. it Will be noted thatthis output circuit ditters from that of tube 18 of Fig. 1 in that one termina-l ot resistance 31 is directly connected to a terminal of resistance l21 and no portion of the. transmission line 11 is included in this circuit.

Two three-electrode electron discharge tubes 5a ano 55 have their input circuits connected in parallel across resistance 31 and have their grids polarized by the common battery 5d. PEhe output circuits ci tubes and .55 are diiierentially connected to the primary Winding 58 of transformer 5 2 and are supplied With energy by a battery 57 connected in a common lead. rlhe secondary 59 ot this .transformer is connected in series with one side or" transmission line 11 and be short-circuited by closing switch. 6G.

Tube 3e in this figure serves the same pur- ',oose as the corresponding tube of Fig.. 1.

A The amplitier() has the values oi its various elements so adjusted that when a given voltage across-the primary 6l of transformer 51 is exceeded, a voltage'is induced in the secondary or 'this transformer which acts in the manner described lin connection with aniplier 1G to block the tubes 54e and 55 (see ifig. .7) oi"- the last stage. r-the eiligect of this is to open the circuit of primary 58 of transrmer 52. The transformer 52 is preferably construeted un, its windings tightly cou P cz.

pled whereby when tubes 54 and 55 become blocked the impedance ci the secondary59 is increased to suchk afvalue as to substantially prevent a dow et current in the transmission line 11.

' in order to uti-lise amplitier 50 as a means or protecting line 11 against .excessive curn rent, it is :only necessary to move switch 22 from contact 8 to contact 9. "jheinput cir,- cuit of tube 1'? is thereby disconnected from transformer 51- and connected to transformer 57, the primary of which is connected rin scries with the transmission line 11. proper adjustment of the constants ot the ampliier 5G, it may be caused to respond to critical value of current in the primary transformer 67, and' introduce a high impedance into the transmission line by means transformer 52, whereby the flow ci" curi bis substantially blocked.

will be noted in connection with and 2 that resistance 21 is comme input circuit ot tube 17 andthe ou cuit ci tube 18 whereby energy'is transferred from this output circuit to theinput circuit. Resistance 21 may be adjustableso that the amount of energy :ted back may be controlled.,

it has been found that with certain values o;

resistance 21,' the ampliers 10 and 50 may be made sensitive to certain critical values ot impressed electromotive -torce or current and may be caused to give greatly increased amplification.

Fig. 3 shows the application oi' the ampli;

tier ot this invention to a signaling circuit. A battery 63 shunted by a resistance 6e may be connected to or disconnected from the input circuit of amplifier 65 by means oi `key 65. rihe impulses produced by lrey 6G may be received by an indicating, device 38 which may be, for example, an electromagnet having an armature or a telegraph sounder.

The amplifier 55 comprises three-electrode vacuum tubes 17, 18 and 69 connected inA series and resistance coupled. Theoutput circuit of tube 18 and the input circuit of tube 1'? have a resistance 21 in common whereby energy may bc Jfed bach -from the output circuit to the input circuit.

"Bube 69 has its input circuit connected across resistance 31 in the output circuit oi tube 18. The output circuit or" tube 69 comprises a battery 70 in series With a relay wind- 71, the armature or' which controis the indicating instrument 33.

The amplifier 55 is adjusted to be responsive to a critical electromotitf'e torce in its input circuit, and the resistance 6a and battery 33 are of such vaines that when key 66 is closed, this criticai elcctromotive force will be exceeded. Assume for example norma? poiarization orn the grid of negative less than the criticai negat izing M. The normal space c tube tvili cause volar- "it of between theiterminals of theexternal series negativepolarization of the grid of tube 18.'

L closed, it will cause a resistance in such direction as to increase the This in turn will determine the magnitude I of the space current of tube 18 and hence the potential difference between the terminals of resistance 31. This potential difference 1s,

however, insuliicient when opposed= by the.

normal C batterypotential of tube 69 to' permit space current in tube 69 ofmagnitude sufficeint -to operate the electromagnet 71. It, 1

with conditions as described, the key 66 be sistance21, which adde to the normal polarization of 'the grid of tube 17 will exceed the critical 4electronaotive force, the space current' of tube 17 will fall below normal value, the. negative polarizing potential ofthe grid of tube 18 will be reduced, and the space current of tube 18 will consequently increase. Theincreased potential difference betweenthe terminals of resistance 31 occasioned bythe increased spacedcurrent is then' sutlicient to make the grid of tube 69 positive or ,at least less negative, with the result-that the space current of this tube exceedsthe value of the operating current required for the magnet 71. This eiiect is, ofcourse, augmented by the regenerative coupling of tubes .17and 18 through resistance 21. Consequently, an amplified current is produced inthe' output cir' cuit oftube-69 Which operates relay l71 and .energizes indicating device 38 to produce an audible or other signal.

Fig. 4 illustrates another application of the amplifier 65. In -this :figure,device 38 is shown as a circuit -breaker arranged to. disconnect-a generator 13 from the transmission line 11, when the key. 6 6-is1closed. Circuit breaker38 may also be 'operated by theaction of'excessive 'electromotive forces or currents in the transmission line 11' by operating the proper combination-of switches 71, 72, 73 and.74, the effect ofwhich will be understood from the explanation given in'connection withFig. 1. The block.7 5 represents the portion of thecircuit of Fig. 3 included with- 'in vthe broken lines.

. In Fig. 5,'.the applicationiof this invention to the analysis of waves is illustrated. Block 77 represents any source of `electromotive force or current to be analyzed. 78 is a po-v tentiometer arranged to be connected .in` place of source 771by means of switch 79; In Fig. 5 an amplifier 80I is arranged in accordancewith this invention to be controlledby source 77 for supplying energy to a solenoid81 which operates -a curve tracing device 82 anda slide Wire potentiometer 83. Between the'amplifier 80 and the solenoid 81 is connecteda second amplifier 85-which is controlled by a source of plies energy directly to solenoid 81.

The amplifier `comprises three-element high frequency variations 86 and which supelectron discharge tubes 87,88, 8 9 and 90 confpotential drop in re-.

vvariations may be impressed 'crates the variable contact 106 o and bus bar 107.

nected in tandem andresistance couples.

The tubes 87 and 88 comprise an ordinary form of resistance coupled amplifier. Tubes 89and 90 constitute a resistance coupled regenerative ampliier in which the, output. circuit oi tube 90 is coupled to the inputcircuit of tube 89 by means ,of resistance'21. yIn- 'cluded in the output circuit of tube 90 is vthe filament andplate of a resistance 92.

Tandem amplifier is resistance coupled to. amplifier 80 by means of resistance 92.

control tube91 and i x 4v'H13 Amplifier 85 -comprises three-element 'elec-l tron discharge tubes 93 and94. Thef output circuit f tube 94 and the input circuit of tube -93 have a, resistance 95 in common by which they are coupled. Control tube 91 has' an' input circuit connected to its filament `and grid which'includes a potentiometer 95 and a resonant circuit comprising a condenser 96 and one winding 97 of a variabletransformer 98. A'source of high frequency alternating current 86 is connected to the other winding potentiometer 83 which connects to resistance wire 112 and bus bar 107.` Plunger 105 .is also arranged to actuate the arm or stylus 108. The end o f stylus 108 may carry a pen or pencil in contact with the sheet 109 passing over a roller 110 at right anglesto the movement of the stylus.

Potentiometer 83 comprises a variable resistance 111 in series withslide Wire 112, va-

' riable resistance 113 and battery 114. This potentiometer is connected in seriesito the input circuit of tube 87 by a variable contact 115 On the input circuit of tube 87 resistance 118 and shunt resistance 119. The source-77 is connected across resistance 118 and serves to introduce variations in the input circuit'oi tube 87. Amplifier 80 has the values ofits resistances grid polarizing batteries'and plate batteries preferably adjusted to such values that with source 77 disconnected and with battery 116 normally connected, a normal space current is produced in the output of tube during the periods when'tuheeQl-Tis condgting. It will lbe apparent upon a' consideration of the circuit that the stylus 108 under slide' wirev there isalso Vincluded a-battery 116,- switch 117, variable the opposing-forces of the springl and the attraction ot solenoid 81 will assume some normal position. An increase in the negative potential of the input circuit or" tube87 will cause an increase oi' current in the output circuit ot' tube 00. r1`his causes plunger 105 to move farther within solenoid 31. rlhe plunger moves the contact'106 along slide wire 112 in a direction which causes a positive increase in the potential ot the grid of tube 3? and thus causes a decrease in the current in the solenoid. By varying the value or battery 116, the normal positionof the stylus may be changed. Likewise by connecting source 77 of varying electromotive force 0r current, to the input of `tube 87 a variation in the potential ot the grid of this tube will be effective in producing corresponding movements of the stylus 1.03 and since the paper strip 109 moves atright angles to the motion of the stylus, a curve representing the wave form ot the source i7 willl be produced thereon.

@n account of the inertia ot the solenoid plunger and its associated apparatus there may be a tendency under certain conditions for the system to oscillate or vibrate. 1n order to prevent such vibration a source or" alternating current 3 6 is caused to introduce a high frequency interruption in the output circuit of tube 90 and consequently in the current supplied to solenoid 31 by alternately blocking and unbloclring tube 91. Thus a series oi pulses instead ot a single prolonged pulse are transmitted to the plunger 105. ylhe plunger is thus drawn gradually to its final position in a series ot steps such that its inertia or momentum is ineective in producing any oscillation or vibration oi the mechanical system. nthe cccct of tubo 91 may bc considered as analogous to a damping agent.

The frequency or" source 36 is preferably high with respect to the natural period of mechanical oscillation of the system of solenoid 81. The electromotive force of the source 86 .is preferably suiiiciently large to alternately shift the resistance of tube 91 @maine-rei# mum to aminimum value.f (See 1 and -lig. 7 respectively.)

ltidesired, a high frequency mechanical interrupter may be substituted tor tube 91 and source 33.

rlhe electromotive force of source 'Z7 may be compared with the known electromotive force Jtrom a standard source '2'8 by operating key 72 and by adjusting potentiometeif'l By means of switch 111", battery 116 may be disconnected from the input circuit ot tube 3'?.

rlhe plunger 105 ot solenoid 81 may be provided with a strong restoring spring. The weight of the moving parts including the plunger 105, brush 106 and stylus 103 is made preferably small as compared to the 'friction torce or current is connected by switch T9 across variable resistance 118. Potentiometer 73 may be substituted for source '17 by throwin switch 79 to contact 2.

` t attery 116 may be cut out oi circuit by throwing switch 11'? to contact 3.

Y Slide wire potentiometer 33 may be adjusted to vary the potential applied to the grid ci` tube 125.

1.7 ariable resistance 113 may be vary the potential impressed on th cuit ofi tube 125 by source 77.

yllhe output circuit ot amplifier 134 may be traced as follows: plate electrode ot tube 126, battery 12'?, closed contacts of switch key 123, filament of tube 129, plate ot tube 129, resistance 131, resistance 21 to filament and plate oi tube 126.

Tubes 132 and 129 constitute a second amplitier 135 having its input circuit connected to source 'T through a phase shifting circuit 133.

The input circuit ot amplifier 135 includes a resonant circuit consisting of a variable condenser 136 shunted about the winding 13'? of the variable transformer 138. The other winding 139 of transformer 133 connects to the output of phase shifter 133. r1`his shifter 133 may consist o't a networlr including inadjusted to e i ductance and capacity elements which may be varied to shift the phase of an impressed electromotive torce by any desired amount.

r1 resonant circuit consisting of a variable condenser 141 in shunt to the winding 142 oi Vthe transformer 13 is coupled to the second winding 1114 of transformer 1413 which is in series with a' variable condenser 1115 and source 7'?. Y

By proper adjustment of the various eler entspr the phase Vs'liiiteif'circii '133 and condensers 1115, 141, and transformers 1113 133, any desired component ot the energy ot source 7? may be selected and impressed upon the input or amplilier By these means also the current output trom tube 129 r be caused to have any paese relation a iatever with respect to that orp the current output of tube 125. ln amplitier l input across device as, tor er is connected to Resistance 21 is so adjusted nput cir- 134 isgonithe verge of instability. Battery "-f n116 1 1" 1aybe introduced to change the potential of the grid of tube 125. This potential may be varied also 'by potentiometer 83. The value ofthe grid potential of tube 125 may be adjusted by this potentiometer so that the amplifier 134 may be triggered when the po tential introduced by source- 77 reaches any l predetermined instantaneous value. I 'lube v 129 which has its output electrodes connected in series with the output circuit of tube 126 may be caused to block the iioW of current in this output circuit by having a sufiiciently negative potential impressed upon j its grid electrode (see l'Fig. 7). The amplifier 135 preferably has its elements adjusted 'so that tube 129 is`normally blocked but is rendered conducting when the varying electromotive force 'or' current of source 77 reaches its maximum value. The time at which tube 129 becomes conducting may be caused to occur at any desired instant in the AAcycle of Athe impressed Wave 77 and consequently in the cycle o'flvariation in the output current of tube 126 by adjusting the elements of phaseshifter 133 as already described.

When -the outputV circuit of tube 126 is n rendered cpnducting'lcurrent passes through resistance 131 and prdduces a change o f potential on the inputcircuit of tube 147 with a resulting change of current in the output circuit of this tube. This change of current will cause a corresponding deflection in the indicating device 148, showing that the predetermined instantaneous value of potential to which the amplifier 134 was adjusted to be responsive has been reached or exceeded. The value of potential actually reached during the instant may be determined by adjusting potentiometer 83 and repeating theeoperation untilftlie amplifier just fails to respond and then vthrowing switch 79 to contact 2 and adjusting potentiometer 78 -to obtain the same condition.v j 7 In order to render the circuit of` Fig. 7 operative, key 128 must first be closed. Open- -ing this key stops the loperation of the system. .f 1

By shifting .the phase of the ivavc iinpressed on amplifier 135, the instant at which tube 129 becomes conducting may be shifted to various points in the c ygzle of variation in the Wave from sgurcerhieliisingxress ,Il .Jxkl j onvamplifie-r 1-34 and corresponding` indi" tions obtained-inthe .device'148 To 'zus way, the wave form of the source7-7 may be analyzed from instant to instant.

This'wave analyzer may bc made respon- 'sivezto very sharp peaks of short duration in the Wave of source 77 by rendering tube Y129 conducting for only a very brief interval of time duringV each cycle of the input wave. This is doneby adjusting thc potential of the -Y--grid of tube 129j.toa value such that it will i remain blocked'feceptat the instant when the Wave of source 77 reaches its maximum amplitude.

Fig. 7 isa grid-voltage' plate-current charateristic curve of the three-electrode' vacuum tubes utilized in this invention to which reference hasbeen made throughout the preceding description. Point 1 indicates a`condition vvhen the grid ofa tube is sufficiently negative so that no plate current flows. Point2 indicates a grid potential of such value that very little plate current iiovvs but that a slight positive increase in the potential of the grid would produce a substantial flow of current. Point 3 represents a value of grid potential such that a flow of current is producedin the plate circuit of the tube. It Will be noted that at this value of grid l potential, the tube is operating upon `the straight portion of its charactertistic. Point 4 represents a grid potential which causes a maximum plate current to flow.

The particular embodiments of this i11- vention which have been illustrated and de- 'scribed aremerely representative of specific application of the principles involved and are not intended as limitations upon its scope.

What is claimed is 1. The combination, in an energy transl lation system of a source of electrical energy, a transmission line connecting said source and an energy consuming device, and means under control of a thermionic amplifier associated with said transmission line for variably controlling the' relation of said source of electrical energy to said line proportionally as the amplitude of an-impressed wave 2. The combination in a system for transmitting electrical'energy of'a sourceof electrical potentiahla transmission line connected to saidsource, an energy consuming device connected to -said line, and means under the control of the current in said transmission linefor variably affecting the relation of said source and said device proportionally as the amplitude of a Wave transmittedtherebetween, said means including athermionic am- .plier adapted to be directly controlled by the current in the transmission line.

nwombmation, an electrical energy j supply source, a trrslation systemV therefor, means for controlling t e re 'ation-6fm said source to said system, said means including a thermionic amplifier, saidv amplifier having its output .circuit'connected in energy transfer relation to its input circuit in such manner thatregenerativeacton may progressively build up its input current when a threshold value of inputV potential is im= pressed, and means energetically associatingsaid -input and output circuits respectively to said source, and to'said translation system.

In combination, an energy supply source, a translation system therefor, and means for amplifying electric energy Whose Output cir- 130 cuit includes a part in commonwith said translating system and Whose input circuit 1s energetically related to said source, sa1d means including a plurality of three-elec-'- trodefvacuum tubes connectedin series, and means for supplying energy from the output circuit of the lasttubenf the series to the input circuit of the first tube of the series, said means including a resistance which may be adjusted to cause the action of said ampliiier to'become unstable.

In witness whereof, I hereunto subscribe my name this Z'Zth day of September A. D.,

JUSTINv L. FEARING. 

